SlipSmart provides Slip Resistance Testing of flooring surfaces to Property Owners and Managers. Slip/Fall incidents are one of  the main causes cited in personal injury litigation. Slipping, tripping and falling accidents account for a significant proportion of the accidents that occur in public places. Accurate measurements of your pedestrian surfaces on a regular basis indicate when remedial action is needed to help reduce the likelihood of an accident.  SlipSmart Pty Ltd specialises in Dry Slip Resistance Testing as well as Wet Slip Resistance Testing. We are fully accredited by the National Association of Testing Authorities (NATA). We are also the sole Distributor of the SlipAlert Slip Indicator for Asia Pacific Region.

Serving Sydney, Brisbane, Gold Coast, Sunshine Coast, Melbourne, Adelaide, Perth, Darwin, Cairns, North Coast.

0410 657 399  www.slipsmart.com.au

Editors Note: We regularly use and can personally recommend SlipSmart testing, consulting and remediation services. We like to call them the "floor safety gurus". Be sure to tell them we sent you - Riskex Pty Ltd.

Articles:

• Summary of Current Australian Slip Testing Standards

• Legal and Practical Aspects of Problems Arising from Slippery Floors

• Slips and Falls - Some arguments about measuring Coefficients of Friction

• Slips, Trips and Falls Guide - QLD Workplace Health & Safety

• Guide to preventing slips, trips and falls - Comcare

• Slips, trips and falls in Schools

• English Court Case - Aged Care Facility

• Assessing the slip resistance of flooring

• Australian Ecolabel Program - Cleaning Services

• Australian Ecolabel Program - Hard Floors

• Ceramic Tile Problems

• Controlling Slips and Falls in Restaurants

• Safe Floors in Health Care Buildings

The following information was provided by Peter Vournechis from “Australasian Slip Testing”.

With more than 30 years experience, Peter Vournechis is recognised as an expert in the highly specialised fields of slip testing, terrazzo and surface cleaning. A founder and Director of Australian Slip Testing Pty Ltd, Peter provides slip-testing and hard floor consulting services to some of Australia’s largest retail and commercial property owners.

He sits on various industry committees including Standards Australia Technical Committee BD-094 Slip Resistance of Flooring Surfaces, is a Platinum Member of the Building Service Contractors Association of Australia and regularly consults to professional associations including the Cement and Concrete Association of Australia.

Firstly I will touch on the frequency of wet and dry slip testing which is a question that everybody asks, in many cases that is negotiated between the insurance company, the owners and testing house. The majority of my clients require monthly dry testing interior and quarterly wet slip testing external. The reason they require monthly interior dry slip testing is because the pedestrian floor surface is regular stripped an sealed, types of sealants do vary the slip resistance of the floor surface and if the floor is not maintained correctly the sealant will exfoliate and cause problems. One of our clients manages approximately 40 shopping centres, they have commissioned Australasian Slip Testing to perform monthly dry slip tests and quarterly wet tests, they also stipulate in the cleaning contract (cleaning contractor controls the slip resistance of the floor) that they require a 15 to 20 min turn around from the staff that maintain the floor surface during trading hours. Most cleaning companies do install movement tracking devices in buildings, this is a hand held device the size of a mobile phone which is carried around by cleaners, individual numbered silicon chip buttons are installed around the premises. These electronic logbooks are commonly called “Wands” and they can generate reports to show whether or not the set criteria has been met.

Maintenance

In many cases service providers such as cleaning companies reduce the service requirements of the premises to obtain the cleaning contract, which reduces the presents of cleaners checking for contaminates on pedestrian surfaces and unfortunately increases the likelihood of someone slipping.  Perhaps the most important step is overlooked which is the exfoliated sealant dust from burnishing, plaster dust from refurbishments, air-conditioning dust on start up and wind that blows contaminates into the premises, all this adds up to a very hazardous pedestrian surface. Then you have the water which is walked into the building by pedestrian footwear/umbrellas, which turns the floor surface into a cocktail of contaminates, the addition of water turns the contaminates into a type of paste and will cause pedestrians to slip especially if rushing in or out of the premises. Regrettably, some contractors neglect to incorporate those extra few hours to sweep the floor surface before the building is open to the public. The reasons being that the extra hours will increase their contract price and some management companies do like to compare apples with apples, unless there is a valid reason. The extra 2 or 3 hours per night needed to perform a total sweep of a reasonable size centre would increase the tender price. And the amount would possibly put the companies tendering out of the race to win the cleaning contract.

If visiting a shopping centre with a sealed floor between 7.30am and 8.00am, you will see the cleaning staff dusting the dust which has accumulated over night on the furniture, pot plants, public phones, etc. In some cases if the floor is not maintained under the manufacturer’s recommendations and the contractor keeps on applying new sealant onto old sealant, the amount of airborne exfoliated dust will increase.

Surface such as large areas of ceramic tiles or high profiled floor surfaces which are scrubbed nightly, will require a different type of scrubber to remove dirt and contaminants from the surface and grout joints. Cylindrical brush scrubber fitted with a powerful vacuum system is suitable for these surfaces. The disk type scrubber will only skim across the surface and the squeegee will only drag the contaminate out off the grout joints which would partially cover the edges of the scrubbed tiled surface and deposit a light film of contaminate.

A service plan should be in place to assure that the scrubber is correctly maintained, especially the squeegee and vacuum motors so all chemical residue and contaminants are removed from the pedestrian surface. The service records of the machinery should be recorded and filled for reference which may be required in future litigation cases where duties of care issues are in question. Cleaning contractors should also teach their staff to observe and report any changes to the pedestrian floor surfaces. Stripping and sealing floors is a very daunting task at the best of times to experienced staff where patience and perseverance are paramount and takes many years of experience and many sealed floors to achieve. Requirements that experienced stripping teams are aware of such as install splash skirts to the high speed propane stripping machine in order to stop splash back on window frames, windows, roller doors, walls etc. When stripping and sealing in a shopping centre complex the tenants that will be effected should be supplied with rags to be places under their roller door to avoid stripper from damaging carpet, timber, vinyl and tiles. After stripping the floor a disc type scrubber fitted with stripping pads is used to remove the dissolved sealant and stripper from the floor then a neutraliser is applied to the surface to remove any residue. Applying the sealant is as important as correctly stripping the floor, the correct consistency in thickness of coats and the amount of coats is very important to the wear of the surface. Manufacturer’s guidelines should be adhered to and chemicals recommended should be used. The strip and seal process is usually carried out once a year depending pedestrian traffic flow. Additional scrub back and reseals are carried out every quarter usually after the school holidays.  

Another type of potential hazard that can be invisible to the naked eye would be the overspray of aerosol or pump spray furniture polish when being directly sprayed onto the timber surface, which also settle on the floor and is extremely slippery especially dangerous if the furniture is moved to another position. Cleaners must be shown the potential danger of this overspray and trained to spray the polish onto a cleaning rag and then applied to the surface.

This is one of many examples of how slip testing can assist Property Managers, Property Owners and insurance company’s in finding the cause of a slip/fall. During our periodical slip audit at a Shopping Centre in Coffs Harbour, I received a call at approximately 4.00pm from Security at a Shopping Centre in Surfers Paradise, requesting an urgent slip test to be performed. Apparently an elderly gentleman had slipped and was taken away by ambulance. I requested Security to instruct the cleaners not to clean that area and to place “witches hats” where the incident occurred. We arrived at the Centre in Surfers Paradise at 9.30pm and performed the dry tests inside the boundary where the incident occurred. The slip tests results were below the recommended coefficient of friction as set out in AS/NZS 4663:2002.

It appeared that there was an invisible contaminant on the floor surface. We also carried out tests on the outer boundaries of the contaminated area for comparison and established that higher results were achieved here. I then asked the shift leading hand for the cleaners, whether the cleaning product that they clean the floor with was altered in anyway; he informed me that they have been using the same product for 3 years. While I was speaking to the cleaner, Security arrived for a credential check which gave me a chance to ask the security guard that was on duty the previous night whether any contractors carried out any kind of work on-site in this area on the previous night. he informed me that the occupant of the tenancy where the incident occurred was in on that night to clean his shop front exterior wall tiles; the tenant firstly applied methylated spirits to the tiles then pressure pack sprayed silicon sealant on the tiles. I asked the security guard to write his observations in a report and I would include his comments in my report. Through the observation of security and the slip testing, the Centre Management passed the claim onto the person responsible for contaminating the pedestrian surface which caused the incident.

There are many instances where temporary leased areas in shopping centre’s have caused problems, especially when cleaning product are used to prepare the items for sale or display, one very dangerous product is “Armour Oil” on tyres, the contaminate is invisible to the naked eye and may cause the sealed floor to be slippery when the temporary leased area is vacant and the pedestrian traffic walk over the area.

Construction

This example is how one hand doesn’t know what the other hand is doing, a very large construction company was in the final stage of handing over a large office and residential building in Brisbane. Company’s and residents had moved into the building and were trading with a fully operational coffee shops and reception on the ground floor, one week before the final payment was made to the construction company received a solicitors letter stating that a pedestrian had slipped on the floor surface in the foyer and all payment would stop until the slip/fall matter was finalised. The construction company started a witch hunt to see who was responsible for the selection of the floor surface and whether slip tests were carried out after the installation of the pedestrian surface, they contacted architects, tile suppliers and tile layers unfortunately there were European test but no Australian Standards tests were carried out. I received a call from the project manager of the project requesting a slip test to be carried out on the ground floor of the building, I requested a single tile to be on hand for a visual comparison, we arrived on site and met the project manager and started our testing, the method used to test the surface was from Australian Standards AS/NZS 4663:2002 Appendix A Wet Pendulum Test Method, I found that there was a need to carry more swings on the pendulum to receive a regular reading which only means that there was a contaminate on the surface. I finally finished the testing which took 2 hours instead of one hour and found that the surface slip resistance had met the recommendations set out in the Australian Standards. I asked the project manager whether I could call in to the site at night to observed the cleaning procedure in place which he agreed, I arrived to see the cleaner using a mop to clean the foyer which was only spreading any contaminates which may be present on the pedestrian surface, I then asked the cleaner whether he was supplied with a scrubber to clean the pedestrian surface, which he replied yes, but it had broken down and has been out of action for about 2 weeks. I completed my report and sent it of to the construction company. We presently test this surface periodically and have found the surface to meet the requirements set out in the Australian Standards, fortunately the scrubber has been fixed and regular maintenance is carried out on this equipment with report sent to the owners. This only proves that the maintenance of a pedestrian surface is paramount to the slip resistance of the surface and maintenance programs should be in place to maintain the slip resistance.

Please feel free to contact me if you need assistance with any maintenance programs or slip testing in general.

email: aussliptesting@iprimus.com.au 

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Summary of current Australian Slip Testing Standards

The present slip testing standards are as follows:

AS/NZS 4663:2004. Slip resistance measurements of existing pedestrian surfaces.

Appendix A. Wet Pendulum Test Method. (In-situ and Lab Testing)

Appendix B. Dry Floor Friction Test Method. (In-situ and Lab Testing)

AS/NZS 4586:2004. Slip resistance classifications of new pedestrian surface materials.

Appendix A. Wet Pendulum Test Method. (Lab Testing)

Appendix B. Dry Floor Friction Test Method. (Lab Testing)

Appendix C. Wet/Barefoot Ramp Test Method. (Lab Testing)

Appendix D. Oil-Wet Ramp Test Method. (Lab Testing)

Appendix E. Displacement Volume Test Method. (Lab Testing)

Handbook HB 197:1999. An introductory guide to the slip resistance of pedestrian surface materials.

Chapter 3. Use of AS/NZS 4586 Classifications in Selecting Pedestrian surface materials.

Chapter 4. Which Wet Slip Test should I use as the bases for my Specification?

Chapter 5. General Commentary.

                  Ramp Classifications.

                  Pendulum Classifications.

Chapter 6. Requirements for Ramps and other Sloped Surfaces.               

Chapter 7. Selection of Pedestrian Surface Materials According to the Ramp Tests.

                  Wet Barefoot Slip Resistance.

                  Slip Resistance in Commercial and Industrial Areas. 

The meanings of terminologies used for reporting slip resistance.

Appendix A Wet Pendulum Test Method. (MBPN) Mean British Pendulum Number.

V Class Classification = >54MBPN

W Class Classification = 45-54MBPN

X Class Classification = 35-44MBPN

Y Class Classification = 25-34MBPN

Z Class Classification = <25

Appendix B Dry Floor Friction Test Method. Coefficient of Friction.  

F = ≥40CoF

G = ≤40CoF

Appendix C Wet/Barefoot Ramp Test Method. Angle (Degrees)

A ≥12 <18

B ≥18 <24

C ≥24

Appendix D Oil-Wet Ramp Test Method. Angle (Degrees)

R9 = ≥6 <10

R10 = ≥10 <19   

R11 = ≥19 <27

R12 = ≥27 <35

R13 = ≥35

Please keep in mind that Australian Standards AS/NZS 4586:2004 was generally designed for laboratory testing in controlled conditions and Australian Standards AS/NZS 4663:2004 for In-situ Testing.

Handbook HB 197 illustrates tables required for both standards and specific location recommendations with conversions.

Reference HB197:1999 Table 3 Pedestrian Flooring Selection Guide-Minimum Pendulum or Ramp recommendations for specific Locations

Reference : AS/NZS 4663:2004 Slip resistance measurements of existing pedestrian surfaces.

TABLE 2 Interpretation Of Dry Floor Friction Results

The term notional has been used to highlight the need to consider all potential contributing factors to a slip incident.

Note: for a ‘Moderate to very low ‘interpretation, each individual test result shall be equal to or greater that 0.35.

Reference: Australian Standards AS/NZS 4663:2004.

In late 2006 at our Standards meeting in Sydney we instigated revisions and amendments to AS/NZS 4663:2004, AS/NZS 4586:2004 and Handbook HB 197:1999. You may ask why I went through the trouble of explaining the old Standards in this document, the reason being that you need to grasp the terminologies of the old Standards to relate to the new. At our last Standards meeting in Melbourne we reviewed the results from the Postal Ballot/Draft for public comment that was sent out in late 2006 and found strong opposition from the industry concerning the introduction of a residential slip resistance recommendations, so we withdrew our recommendations for the residential sector. The following are the amendments to AS/NZS 4586:2007 and AS/NZS 4663:2007. The new Standards will be available in late 2008.

AREA CLASSIFICATIONS

· Dry areas  those areas in which appropriate control measures ensure an area remains dry when in use.

· Transitional areas  those areas that are intended to be kept dry, such as by the provision of design features (awnings, drains, mats, air locks etc.) appropriate to the physical locations, climate and general exposure to water as maintained in a dry and clean conditions by the facility manager.

· Wet areas  those areas that are not defined as a dry or transitional areas, which may be either constantly or intermittently wet or otherwise contaminated.

TESTING RUBBER: NEW CLASSIFICATIONS FOR PENDULUM TESTING

The Standards Four S rubber is now also known as Slider 96. It was developed as a rubber of average slip resistance characteristics. When assessing products for wet barefoot areas, or unusually rough products, the use of the softer more malleable TRL may be advantageous. The TRL rubber is now also known as Slider 55.

AS/NZS 4663:2007. Slip Resistance Measurements of Existing Pedestrian surfaces.

Appendix A. Wet Pendulum Test Method. (In-situ and Lab Testing)

Appendix B. Dry Floor Friction Test Method. (In-situ and Lab Testing)

Appendix C. Surface Roughness Method of Testing.

Appendix D. Examples of Determining Slope Design Value (SDV) and Slope Correction Value (SCV)

Slip Resistance Value (SRV)

The SRV is the mean BPN value for the sample that has been tested, regardless of whether the surface was level or on a slope.

Slope Correction Value (SCV)

When the slip resistance of a sloping surface of known maximum gradient is measured, the SCV is an adjusted SRV, giving a value equivalent to that of the equivalent SRV for a level surface.

Slope Design Value (SDV)

The SDV is the mean BPN value required of a known maximum gradient. The SDV may be calculated by using the tables that are given in Appendix D, using the minimum SRV that is considered appropriate for a level surface.

Reference to Australian Standards

AS/NZS 4586:2004

AS/NZS 4663:2004

Handbook HB 197:1999

DR 07067to revision of AS/NZS 4663:2004

DR 07066to revision of AS/NZS 4586:2004

 BACK TO TOP

LEGAL AND PRACTICAL ASPECTS OF PROBLEMS ARISING FROM SLIPPERY FLOORS

R. Bowman

CSIRO Division of Building, Construction and Engineering
PO Box 56, Highett, VIC 3190
Facsimile +61 3 252 6244

INTRODUCTION

I would like to thank you for the invitation to speak, the kind introduction and for the challenging title of my presentation. Whilst studying at University, the assignment that gave me most satisfaction was assessed as a failure, because the examiner could not conceive that it could be completed in any way other than he had expected. As we shall see, perception is a very important aspect of how we approach slippery floors, whether as pedestrians or litigants. In trying to fulfil your expectations in this highly complex area, I will endeavour to present sufficient information without overloading you. I recognise your diverse backgrounds and interests, but I do not intend to direct specific comments at any segment of the audience. It is important that the legal fraternity learn the basis on which architects select flooring materials, and that the building industries appreciate aspects that may prove critical in litigation.

I don't intend to get too technical tonight. I will attempt to present material as simply as possible, purposely overlooking many advanced modern theories that may be considered to be the field of the specialist consultant. However please remember that many factors will have multiple influences, some of which may not be discussed. Let us consider two glass slides held together by surface tension such that they cannot be pulled apart. The water that holds the slides together in tension can act as a lubricant enabling them to be separated in shear.

PERSONAL BACKGROUND

First, a little bit about my background. I am a ceramic engineer, that is a materials scientist who specialises in the production and uses of ceramic materials. I have been responsible for ceramic tiling matters within the Division since 1982. I chair the Standards Australia committees on ceramic tiles, fixing of ceramic tiles, ceramic tiling adhesives and slip resistance of pedestrian surfaces. My principal research interest has lain in the moisture expansion of tiles, and differential movement failures. I have been involved in several pop-up investigations on behalf of a diverse range of clients. I have acted as an independent technical expert witness in such cases, but not in relation to slip resistance. I have briefed a number of solicitors and barristers on slip resistance, but have not been called upon to appear. A large number of these matters appear to be settled, and I understand that there is relatively littlecase history.

BACKGROUND TO SLIP RESISTANCE TESTING

This presentation coincides with the imminent release of AS 3661 Slip Resistance of Pedestrian Surfaces, Part 1: Requirements. Before outlining its history and contents, I will provide you with a background to slip resistance testing. This will facilitate a subsequent discussion of how one should assess the slip resistance of floors, and how allowances should be made for several very important factors.

Prevention of slipping accidents requires the provision of adequate friction through the use of suitable combinations of shoe soles and floors. My given title presumes that problems arise from slippery floors. It did not allow for the very likely possibility that accidents may result from an inappropriate choice of footwear.

Friction is a straightforward concept, and its measurement would at first seem to be a simple matter. Coefficient of friction (COF) is defined as the friction force opposing sliding motion divided by the force normal to the surface. However, many factors have a significant influence on the friction between shoes and flooring surfaces. Ergonomic studies have indicated that people walk very differently. Most peopledemanda COF between 0.25 and 0.3 when walking normally. People who walk with long fast strides have a higher friction demand. However, we can quite successfully walk on ice and other slippery surfaces that provide very low COFs. When we perceive a potentially dangerous floor, we shorten our stride and walk slowly. We also do this when we walk down a steep slope.

Safety considerations demand that there should be a COF of at least 0.4 available between the shoe and the floor. This measurement must be made under realistic conditions, including the presence of contaminants on the floor if they cannot be avoided. The resulting measurement is peculiar to the shoe/floor/contamination situation. When we consider that there are several shoe materials and design features, floor materials and surface profiles, degrees of wear and cleanliness, type and amount of contamination, it can be seen that there could be millions of combinations of such shoe/floor/contamination situations. There is an obvious difficulty in trying to use a single measurement as an indication of the slip resistance of a floor. However, commercial considerations demand that flooring materials be characterised with the minimum amount of testing.

REPLICATING INCONSISTENT GAIT

We all walk differently. Ergonomic studies have indicated that the maximum friction demand during the gait cycle predominantly occurs at heel strike. This has led to the development of several machines that seek to simulate the conditions at heel strike. While this is logical, it should be recognised that such devices may not adequately simulate other slip conditions, such as a slip when a person pivots on a spot. Conditions that are considered important in simulating dangerous slips are:

• use of a whole shoe or shoes of the type to be worn;

• angle of contact of the shoe with the floor similar to the angle soon after heel strike;

• a vertical force of about half body weight;

• rate of application of the vertical force;

• realistic slipping speed; and

• testing with typical contaminants on the flooring.

Many devices have been developed for determining COF. These can be categorised according to whether they measure static or dynamic COF (or both), and whether they are portable and capable of being used outside of a laboratory situation. There is unfortunately substantial inconsistency both between these devices and people's perception of how safe they feel when they walk. The latter experience is a reliable indicator of floor safety, if the subject is conscious of the risk. However, it is generally impractical to have suitably protected subjects wearing test shoes walking rapidly on test floors that have been treated with test contaminants. Such conditions have been simulated in several expensive laboratory-based test machines that have been built combining force plates and articulated feet. Despite their immense usefulness in analysing specific shoe/floor/contaminant situations, such devices were not considered as candidates for the Australian Standard for the slip resistance of pedestrian surfaces.

STANDARDS COMMITTEE DELIBERATIONS

The problem of slippery floors has been separated into two elements, one of assessing floors and the other of assessing footwear. There is a draft Australian/New Zealand standard providing guidelines for selection and care of footwear for resistance, as well as an ISO draft entitled 'Test method and specification for slip resistance of footwear for professional use'. This test method uses an articulated foot. We can assume that it will ultimately be adopted as an Australian standard.

I wrote to Standards Australia in 1985 advising them of the need to develop a standard for determining the slip resistance of flooring materials. However, it was not until 1991, after the Australian Uniform Building Regulations Coordinating Council (AUBRCC) declared their desire to incorporate such a standard in the Building Code of Australia, that a committee was formed. At its inaugural meeting in 1992, BD/44/3 decided that it should produce a simple document, appropriate for the building industry, with compliance requirements in the standard and the designated test methods in appendices. As far as testing devices were concerned, consideration was limited to the use of the horizontal pull slipmeter (HPS), the Tortus floor friction tester, the Stanley pendulum, and the inclined ramp test. [The first three devices were on display, and have been extensively described in the literature. The ramp test, being a laboratory based test that uses human subjects, could not be displayed.] It has been included in the draft ISO standard for determining the COF of ceramic tiles, and has long been used within Germany as the basis for ensuring that floors comply with insurance industry requirements. Where enhanced slip resistance is required, ISO/TC 189 has established draft dry and wet compliance limits for ceramic tiles. These are 0.4 for dynamic COF using the Tortus, and 0.5 for static COF using a static method. BD/44/3 rejected the use of the HPS, which determines static COF, because dynamic measurements are more widely accepted to be indicative of slip resistance. While the static COF generally exceeds the dynamic COF, falls actually result from movement of the shoe across the surface. Therefore, the lower dynamic COF should be considered as the controlling factor that must be overcome by muscular reactions in order to regain or maintain balance. ISO/TC 189 has classified tiles with COF results less than the above compliance limits as 'satisfactory for normal installations'. This reflects the fact that several such products have been successfully used in domestic bathrooms. It was considered inappropriate to prohibit such products, when one's behaviour is typically conditioned to their use. People use bath mats to maintain the floor in a dry condition and they walk slowly.

ISO/TC 189 propose to use the (Tortus) floor friction tester rather than the Stanley pendulum, as it gave better correlation with COF determinations made on the inclined ramp (which is also being incorporated in the ISO test method for ceramic tiles). It was also intended that the ASTM Horizontal Pull Slip Meter test method be adopted, but, after a comparison of 7 static friction testers, it now appears that this test method must be modified to include a calibration procedure. The fact that a calibration procedure must be applied to this relatively sophisticated device has serious implications for those consultants who have been determining slip resistance by connecting measuring scales to weighted shoes. Considering that shoes vary from being flat with one sole material to a high heeled shoe with different sole and heel materials, obvious difficulties can arise from the choice of the amount of load and its distribution, and the manner in which the force is applied to initiate slip. Furthermore such techniques may give high readings due to a noticeable adhesion (stiction) effect, but not always in contaminated environments.

The Australian committee, BD/44/3, regarded the Tortus as simulating the action of pedestrians moving slowly or cautiously across a floor, whereby the tendency to aquaplane in wet conditions is excluded. The high wet COF results for some flooring materials were viewed with suspicion on the basis of experiential assessment. Conversely, BD/44/3 considered the Stanley pendulum to simulate pedestrians running, hurrying or turning abruptly as, when wet, it replicates the aquaplaning effect that is particularly pronounced on smooth or highly glazed tile surfaces. Neither instrument is ideal, but when used together help to give a good understanding of the likely slip hazard of most surfaces. They have thus been adopted in AS 3661 Part 1, but only for use in those conditions for which they are considered appropriate.

The three other major areas for BD/44/3 deliberations related to the shoe materials to be used in the test devices, the conditioning of the floor materials, and the compliance limits. There were essentially two choices for the sensor materials: the Four S (Standard Simulated Shoe Sole) rubber developed by Rapra Technology Limited (Rubber and Plastics Research Association, UK) for use in the Tortus, and the TRRL (Transport and Roads Research Laboratory, UK) rubber used in the Stanley (or TRRL) pendulum tester. James, of Rapra, has compared the performance of the Four S and TRRL rubbers in the pendulum tester. The Four S rubber provides better discrimination on smooth and moderately rough flooring materials, while the TRRL rubber provides better discrimination between very rough pavers and road surfaces. BD/44/3 decided that it was more appropriate to specify a Four S slider that gave better discrimination on the more marginal surfaces, such as those normally used indoors. However, I anticipate that the manufacturers of clay and concrete pavers may elect to use the TRRL rubber for distinguishing very safe pavers from those which may prove troublesome in service. This will eliminate the need to test with two sensor materials as the TRRL rubber is also used for determining the skid resistance requirements for vehicular traffic.

BD/44/3 chose not to specify any surface conditioning treatment to simulate wear. It was recognised that different materials wear in different ways, and that the rate and type of wear can be influenced by the environment and the nature and amount of the traffic. For instance, AS 1141.41, as commonly used in the 'City of Sydney test', produces an abraded surface, which does not replicate the uneven wear brick pavers often experience due to impact damage. Some materials will become covered with moss, while others will become coated with contaminants, including the residue of cleaning operations. It is very hard for manufacturers to determine precisely how and where their products will be used. Thus, AS 3661 states that 'The surface to be measured shall be representative of and in the form in which it is intended for use' and notes that 'it is not intended that the test will take into account any future wear or maintenance of the surface'. Floors intended to be sealed or otherwise treated with a permanent surface coating shall be tested with the coating in place. It is worth noting that products, such as wire cut extruded pavers, may have different coefficients of friction when measured in different directions. Their minimum coefficient of friction is reported.

AS 3661 Part 1 does not cover grating, and states that it 'may not cover some resilient surfaces'. This is because the pendulum test relies upon a loss of energy to indicate its measure of slip resistance, and a resilient surface may adsorb energy. AS 3661 Part 1 also states that it 'may not apply to heavily-profiled surfaces where the surface has been specifically manufactured to be highly slip resistant'. The Standard gives examples of such surfaces in a figure and notes that the inclining ramp test or dynamic test machines may be suitable for determining their slip resistance. One should note that several of these surfaces are designed for specific applications.

BD/44/3 has established slip resistant compliance limits of 0.4 for the wet and dry coefficients of friction. Significantly, the dry COF is identical to that proposed by ISO/TC 189, although a number of interests considered that a higher value would have been more appropriate. Most importantly, it must be noted that AS 3661 Part 1 states 'It is intended that this Standard be used as a test method to establish the slip resistance of a pedestrian surface in either the "wet" or the "dry" condition'. Furthermore, 'Wet areas are all external pedestrian areas plus those internal pedestrian surfaces that are normally wet during use'. The Standard notes that 'It is anticipated that regulatory authorities may specify the areas required to be slip resistant and whether these areas are to be considered "wet" or "dry".' BD/44/3 did not anticipate that domestic bathrooms would be considered as "wet" areas since bathrooms are normally maintained in a dry condition through the use of bath mats. With this in mind it included the note that 'Water should be excluded from all dry areas, for instance by the appropriate design of entrance foyers'.

LEGAL ASPECTS OF SLIPPERY FLOORS

I trust that this serves as a useful introduction to some of the practical aspects associated with slip resistance, and particularly those related to the new Standard. However, in considering the legal aspects of slippery floors, one must first consider the deficiencies associated with the standards and the way in which they have been used. Standards generally represent a compromise agreement of the most suitable and best practice available at the time. In most instances we know that the draft standards are capable of further improvement, but as refinement comes at the cost of time, a decision must ultimately be made to publish. Last year, I published a study of round robin tests on the Tortus. This found that there was high variability between the test results of different operators, both in dry and wet conditions, although it was not clear whether the variability was due to operational procedure, the Tortus, or the manner in which the results are recorded and interpreted. I now believe that there is some variation between machines, as well as the manner in which the results are recorded and interpreted. An Italian manufacturer has developed a modified version of the Tortus that has heeded my call for the means of internally integrating the recording so as to provide a mean result. My initial assessment of this Gabbrielli device is generally favourable. Apart from its weight, it is much easier to use and promises to be quite reliable. Unfortunately, it does not comply with the AS 3661.1 apparatus requirements, in that it weighs more than 8 kg and does not have dimensions of 420 x 236 x 100 mm. It was not the intention of BD/44/3 to exclude variants of the Floor Friction Tester on such grounds, as neither of these requirements are vital to the performance of the Floor Friction Tester. I understand that the original developers of the Tortus are in the process of modifying it, with a view to releasing a new instrument. They need to as their current model also does not comply with AS 3661.1. I anticipate these requirements will be promptly modified. This mishap occurred as a result of closely following the ISO draft.

The FSC 2000 apparatus has been developed to overcome some of the limitations associated with the Tortus. It appears to offer excellent promise. It is battery powered eliminating the need for mains power. It has an internal strip chart recorder that indicates both the static and dynamic frictions. It provides electronic integration of the results. It is factory calibrated and is exceedingly simple to operate. While it determines coefficients of friction in a similar way to the Tortus, it does not comply with AS 3661.1 in that it is lighter, smaller, is battery powered, has a different sized slider mounted in a different way, etc. In particular, its speed appears dependent on the COF as the FSC 2000 runs on two wheels and the slider. Even though it does not comply, it is so simple to operate, that owners and managers of large buildings would be well advised to consider its purchase for routine monitoring of floor condition, and immediate characterisation of specific areas should an accident occur. [Use of the FSC 2000 was then demonstrated].

I further understand that RAPRA, the developers of the Four S rubber, are trying to develop an improved rubber for determining the slip resistance of flooring materials. The UK Slip Resistance Group are also considering the development of a lighter smaller pendulum device more appropriate to determining pedestrian slip resistance. It thus appears that AS 3661.1 will be subject to much revision over the years. In this context it is important to note that the Scope includes the statement 'Other test methods can be used to meet the compliance requirements specified herein, for example test procedures based on force plates'. I thus propose to use the Gabbrielli Floor Friction tester on this basis, where any deviations from AS 3661.1 Appendix B will be reported. Other deviations are often necessary, particularly since some clients cannot provide sufficient test specimens due to problems of supply. The latter may have significant legal implications if the flooring material has highly variable slip resistance characteristics.

HOW RELEVANT ARE THE TEST RESULTS?

A recent British study of the advantages and disadvantages of in-situ methods of measurement for liquid contaminated floors has reported that the Tortus measures some aspect of friction, but that it does not properly assess the effect of aquaplaning on smooth floors, thus overestimating the level of grip. The standard slider is also one of the better shoe sole materials, also giving high grip. The pendulum takes account of aquaplaning on smooth floors, but overestimates the effect of aquaplaning and underestimates the level of grip. The Tortus and pendulum results both depend on the type of slider material and its roughness. Measuring the surface roughness of the floors has the advantage of taking account of aquaplaning on smooth floors, but it does not assess friction between surfaces. The product of the Tortus and surface roughness results was found to give the best correlation with experiential results obtained on the inclined ramp. It has been suggested that COF results are meaningless unless the level of surface roughness is known.

While BD/44/3 have adopted the Pendulum for wet COF measurements, ISO/TC 189 have adopted the Tortus, together with a 0.4 compliance requirement. We may thus expect that, when the ISO standards are promulgated, most imported tiles will have been characterised by wet and dry Tortus measurements. As indicated previously, Tortus COF results should not be evaluated against criteria developed for use with other instruments. Proctor has indicated that, on wet floors using the Four S rubber slider, a Tortus reading above 0.68 is required to ensure safety. Proctor concluded 'The interpretation of the results of measurements of the slip-resistance of floors is very complex. It is clear that architects and flooring contractors need to be advised on correct interpretation, especially regarding the results of the ramp test. This information can only be supplied by the organisation responsible for carrying out the tests and should be included in the test reports.' The latter sentence presumes that the organisation is prepared to accept the responsibility for such interpretations, which may not be the case unless it is presented with a specific scenario. In many such situations, it would be necessary to study the effects of wear and contamination on the change in COF. Proctor also concluded 'None of the methods that can be used in-situ, is satisfactory for assessing floors that incorporate a raised profile. Further developments are urgently required in this area.'

ARE THE COMPLIANCE CRITERIA RELEVANT?

In Britain, the Greater London Council adopted the TRRL (Stanley) pendulum tester and published criteria for pedestrian safety. It appears that the manufacturers of the Tortus have accepted these criteria and adopted them. It is worthwhile reflecting on the fact that the readings obtained with these two devices do not generally correlate, and also that the readings are affected by the type of rubber used.

Given the limitations associated with the available test methods, it would appear preferable to establish classes of materials for specific applications. While these could be based upon coefficients obtained by accepted test methods, manufacturers could opt to downgrade the classification of borderline products to protect themselves against possible litigation. This classification could also consider the reduction that occurs in passing from dry to wet conditions. Products that perform significantly differently when wet and dry are potentially more dangerous than those which generally perform poorly when either wet or dry.

WHAT OF THE FUTURE?

In concluding this part of my presentation, we have a new standard for the slip resistance of pedestrian surfaces. While this will help to focus attention on providing and maintaining safe flooring surfaces, anomalous results will be obtained for several products. This realisation highlights the need for developing improved methods for reliably characterising slip resistance. This may sound more attractive than feasible, given the numerous devices that have been developed over the years. However, research in other fields has given us a better understanding of surface roughness effects on wetting phenomena, and there are a number of improved techniques for characterising surfaces, their interactions, and how they vary with time as a consequence of degradation. Preliminary discussions with potential research consortium partners have suggested that there should be significant benefits to product manufacturers, both of flooring surfaces, maintenance products and footwear, in terms of enhanced products. Specifiers and building regulators will be provided with more accurate data, and building owners and managers will benefit from improved maintenance practices. Safer floors should result in lower insurance premiums, although there is a widespread cynical view that insurance companies do not necessarily consider this to be in their best interests as their business depends on the existence of risk. Occupational health and safety policies demand the prevention and minimisation of the risk of accidents. If halving the incidence of accidents which result from slipping, tripping and falling on level surfaces could annually save Australian industry over $100 million, such research would seem a worthwhile investment.

CHANCES OF A SUCCESSFUL CLAIM

This pertains to the future. Now, let's consider the present and specifically what happens when someone has a genuine accident that is then blamed on the floor. Their chances of a successful claim will often depend on the immediate actions of the person or persons responsible for the area, and specifically the plans in place for such an occurrence. However, in the majority of cases inadequate and inappropriate records are made. Too often, consultants are asked, sometimes years later, to offer an opinion as to whether the floor would have been safe or dangerous, and if dangerous, whether it was ever safe. Even in these circumstances, there is much information that a consultant can generate, although the information gathering process will vary depending on the circumstances, particularly access to the parties involved. Perhaps the best starting point is to determine the factors that should have been considered during the planning and installation. AS 3958.2, Guide to the selection of a ceramic tiling system, contains a flow chart of the process of designing a ceramic tiling system. This emphasises the need to analyse the intended environment and the anticipated conditions of use. When considering slip resistance, one must also consider the likely extent and type of contamination, the volume and type of traffic, the nature of the activities and likely footwear, the configuration of traffic and non-traffic areas, the presence of drains, slopes and stairs, the COF of adjoining floor materials, amongst other factors. The consultant must appraise such aspects together with the condition of the floor as a consequence of design, fixing, maintenance and cleaning. It has been stated (Hughes) that in almost 60% of slippery floors, some blame has to be attached to poor cleaning and maintenance routines. It has been estimated that in Australia, 74% of public liability claims relate to slips and falls, 86% of these incidents were preventable, and that 77% of the preventable incidents related to cleaning practices.

The draft of AS 3661 Part 2, Guide to the reduction of slip hazards, provides guidance on the selection of pedestrian surfaces for slip-resistant characteristics. It does not list general qualitative guidelines on the slip resistance of typical flooring materials due to the large variability in the characteristics of generic products. It notes with regard to indoor flooring that 'the effect of texture in providing slip resistance is dependent on the size and spacing of the texturing. Generally a granulated effect of raised areas 1 mm-2 mm in diameter and a similar distance apart is the most effective. Larger diameters and spacings become progressively less effective.' 'Outside, textured, free-draining, stable materials are suitable.' Until AS 3958 was issued in 1991/2, and before that BS 5385 Part 3 in 1989, BS CP 202, Code of Practice for Tile flooring and slab flooring, was used as the de facto Australian standard. Clause 3.5, Slipperiness, advises 'When it is known that in service these slippery conditions may arise and present a significant hazard, especially where floors are laid to steep falls, advantage should be taken of the slip-resisting finishes and slip-resisting inserts available'. The example for ceramic tiles advises 'clay tiles can be obtained with ribbed and studded surfaces, particled surfaces (shot-faced or pin-head finish) and with non-slip aggregates incorporated in the wearing surface.' It must be recognised that some profiled styles have been designed for barefoot areas such as swimming pool surrounds. As the foot may contour around the tile surface in a way that shoes may not, caution must be exercised in selecting slip-resistant tiles.

In the situation where there have been no Australian standards, one should determine what information was available at the time the flooring material was specified, both locally and overseas, in order to consider whether it had been appropriately specified for the intended environment. Did the specifier receive information about the slip resistance of the flooring material, how was the data generated, and was the test method appropriate to the material and the intended environment? The latter questions are particularly important in litigious circumstances, recalling that there may be substantial inconsistency in the COF measured by different machines, and that the compliance criteria developed for one device may be indiscriminately applied to the results obtained by dissimilar test methods.

A common method of assessing the slip resistance of footwear on a specific floor surface has been by means of a drag test, where the minimum drag force required to initiate movement of a shoe loaded with weights is measured with an accurate spring balance. The static COF that is obtained will depend on the load, its distribution throughout the shoe, and the manner in which the drag force is applied, as well as the construction of the footwear. Thus, it is not necessarily an accurate measurement. Primitive drag tests are not highly regarded by the scientific community, although they are apparently still included in some educational curricula. However, if the shoe used was that worn by the injured party, it may have some significance, depending on the circumstances of the fall. It would probably be more appropriate to use the Tortus Floor Friction Tester with a slider taken from the heel of the shoe. This will enable a comparison relative to the Four S slider. The slip resistance characteristics of some sole materials change with wear and with temperature. Leather has reasonable slip resistance when it first absorbs water but poor resistance when saturated. On dry floors, a patternless sole gives the maximum degree of friction, while on wet floors patternless soles show a decline in slip resistance. In athletic footwear, there is commonly a mechanical interlocking of treads into surfaces that adds forces above those of pure friction.

In my introduction, I indicated the importance of perception. Falls frequently occur through lack of perception when people are unaware that the flooring they are about to walk on differs in some way from that which they are accustomed to. Such differences include changes in the COF due to the use of dissimilar floor materials, wear of floor materials or the presence of contaminants, and small differences in the level of the surface due to proud segmental units. A good example of the consequences of dissimilar floor materials can often be observed in grand hotels where guests slip when walking from plush deep-piled carpets to highly polished floors. They will often trip when walking in the reverse direction. Experts must try to determine a variety of relevant extrinsic factors, and assess their possible influence on pedestrian perception.

Given the incidence of accidental falls, it appears that it will only be a matter of time before expert witnesses will be arguing in court about whether or not a particular product meets a compliance requirement. If ISO/TC 189 adopt a dry dynamic COF requirement of 0.40, one might expect that two experts, testing a product with this COF, would be doing well to obtain respective results of 0.38 and 0.42, such is the observed variability. Rounding results to the nearest 0.05, as required by AS 3661.1, will tend to reduce the incidence of such conflicts. However, it may be that where a product has a COF of 0.37, one test house might assess it as such, where it would fail after being rounded down to 0.35, while another might assess it to be 0.38, where it would pass after being rounded up to 0.40. It must be recognised that since the various available test methods that determine the COF using a standard shoe material and specific test parameters,they are only indicative of what may occur in practical situations.

As seen, a variety of causes can influence how and when a fall can occur. A successful defence may rely upon the establishment of an effective slip and fall prevention program, incorporating both design and management aspects into a unified approach. A successful program requires the prevention of falls, and effective claims management and litigation defence. The basic elements of such a program include:

1. Stating a strong policy and getting commitment

2. Establishing a methodology and criteria for review and acceptance of walkway surfaces and related components

3. Reconditioning and retrofitting walkways in existing areas

4. Maintenance standards and procedures

5. Inspections, audits, tests, and records

6. An employee footwear program

7. Aggressive claims management and litigation defence methods

8. Measuring results

CONCLUDING REMARKS

This is a complex area where the results obtained using the recommended test methods are open to misinterpretation. While AS 3661.1 represents the best compromise choice of the numerous available test methods, it appears likely that it will need to be modified as significant efforts are being made to develop further improvements.

Rather than specifying minimum coefficients of friction, consideration should be given to establishing classes of slip resistant materials for specific areas of usage, enabling manufacturers to classify their products as they consider appropriate. This could be based on both the wet and dry coefficients and the effect of changing conditions. Such a classification would have to make assumptions that the product would be properly installed in a suitable environment, and that it would be satisfactorily maintained. There is a widespread need for general education in this complex area. There is little published material to assist specifiers and purchasers of flooring materials in its selection. There is equally little independent material to assist retailers in providing advice. Such advice should be based on a much needed, extensive collaborative research program.

Considerable strides have to be made to limit the costly and painful incidence of falls. Industry practitioners will need to adjust their gait to the reality of their possible exposure to litigation. It appears that until the current uncertainty is replaced with an ordered framework, there will be a continuing call for the services of specialist consultants and the legal fraternity. My personal advice is to not only watch your step, but also to watch what you put your foot into. Some shoes predispose one to accidents. This aspect of self contributory negligence is another issue that has yet to be fully addressed.

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Workplace [Health, Safety and Welfare] Regulations 1992
Ellis v Bristol City Council [2007] Court of Appeal: 5 July 2007

This recent Court of Appeal decision imposes a greater demand on employers by extending the ambit of strict liability under the Workplace [Health, Safety and Welfare] Regulations 1992.

Facts
The Claimant was employed as a care assistant at a home for the elderly run by the Defendant.  The Claimant slipped in a pool of urine left by one of the residents on the main corridor.  The Defendant was aware of residents urinating in the main corridor on a regular basis which made the vinyl floor surface slippery.  A number of accidents had occurred due to presence of urine on the floors. The Defendant had a good system of inspection and cleaning in place, as well as risk assessments, warning notices and 2 non slip mats positioned in the worst hit areas.

The trial decision
The Claimant had pleaded her case under regulation 12 of the 1992 Regulations, alleging the floor was not suitable for the purpose for which it was used because it was frequently urinated upon and became slippery when wet.  Paragraph 93 of the Code of Practice in relation to Regulation 12 provided that surfaces of floors which are likely to get wet should be of a type which do not become unduly slippery and a slip resistant coating should be applied where necessary.  This Code of Practice and alleged breach was disregarded by the judge because it “was not a matter specifically pleaded or dealt with in evidence”.

The judge dismissed the claim on the basis that the strict liability in Regulations 12(1) and 12(2) related to the construction of the floor surface and not to a transient hazard. 

The Claimant appealed.

Court of Appeal Judgment
Regulation 12 of the Workplace [Health, Safety and Welfare] Regulations 1992 reads;

a)         Every floor in a workplace and the surface of every traffic route in a workplace shall  be of a construction such that the floor or surface of the traffic route is suitable for  the purpose for which it is used.

b)        Without prejudice to the generality of paragraph (1), the requirements in that   paragraph shall include requirements that—

• the floor, or surface of the traffic route, shall have no hole or slope, or be uneven  or slippery so as, in each case, to expose any person to a risk to his health or safety;        
  
  and

 Every such floor shall have effective means of drainage where necessary.

c)        So far as is reasonably practicable, every floor in a workplace and the surface of every traffic route in a workplace shall be kept free from obstructions and from any article or substance which may cause a person to slip, trip or fall.

In the lead judgement, Lady Justice Smith held and explained;

1.      The overriding intention of the Legislature when drafting these Regulations was the protection of workers.

2.      In assessing floor suitability, Regulations 12(1) and (2) require the court to consider all relevant factors which will include;            

• the construction of the floor;

• nature / quality of its surface; 

• the frequency and regularity of conditions, such as spillages, arising;

• the purpose for which the floor was used;

• the likelihood of an accident occurring;

• the gravity of any injury which may occur; 

• whether the substance or hazard was obvious to the naked eye; 

• any relevant accident history and / or previous complaints in relation to staff accidents

The court should then “stand back” and decide objectively whether it can be said that the floor was suitable for the purpose for which it was used.

3.      If a smooth floor is frequently and regularly slippery because of a substance which lies upon it, albeit only temporarily, the surface of the floor may properly be said to be unsuitable, if the slipperiness is such as to give rise to a risk of the health and safety of those employees using it.

There had been three instances of workers slipping in urine within the three year period preceding the index accident.  An injury caused by slipping in urine and leading to injuries of at least moderate severity was entirely foreseeable.

4.      Official publications, i.e. the Code of Practice, emanating from the relevant government department can be referred to in civil proceedings as an aid to construction.  Although the Code of Practice should be treated with caution, on this occasion it supported the finding that regularly and frequently occurring conditions should be taken into account when deciding whether a floor is suitable for its use within Regulations 12(1) and (2).

5.      Regulation 12(1) is intended to cover permanent features of the floor and also regularly and frequently occurring hazards while Regulation 12(3) is intended to cover transitory conditions which occur less frequently.  The suitability of a floor must be considered in conjunction with the conditions in which it is used.

The Claimant’s appeal was allowed.  Contributory negligence was assessed at one third with Lady Justice Smith imposing greater responsibility on the Defendant on the grounds that the breach of a provision of strict liability “connotes a higher degree of responsibility”. 

Comment
The decision in Ellis goes further than previous case law, finding that an employer must not only assess the construction of floors and traffic routes but also any transient substance which lies upon them on a regular basis. 

Pre Ellis, in order to escape liability, employers could argue they took all reasonably practicable steps to avoid a slipping hazard by keeping the floor free from any substances likely to cause a person to fall, by showing they had a robust cleaning / inspection system, and warning notices were in place. Post Ellis, employers run the risk of facing a strict duty, with lesser prospects of successfully defending such a claim, if spillages are frequent and the facts of the case fall within Regulation 12(1).  Regulations 12(1) and 12(3) now appear to be mutually exclusive in relation to transient substances - the question to ask is whether the substance lies upon the floor on a “frequent and regular basis”.  If the answer is yes, it falls within Regulation 12(1); if no, it falls within Regulation 12(3).

It is important for authority employers to bear in mind that the duty under Regulation 12(1) is limited to ensuring the floor surface is suitable for the purpose for which it is used.

In developing a strategy, authorities would be well advised to;

1          Assess the purpose for which the floor is used, who uses it and the likelihood of spillages;

2          If they consider the floor is slippery, it should be replaced with a non slip surface.  Although this may seem an expensive option, the total costs of one fast track claim could be in the region of £20,000 - £25,000;

3          Introduce and supervise a robust inspection and cleaning system;

4          Warn employees of any dangerous or slippery surfaces;

5          Erect warning notices in the vicinity of the dangerous or slippery surfaces; and

6          Instruct employees to report and / or clean any spillages immediately.  A record of such incidents should be maintained to enable statistics of ‘frequency’ to be compiled.

Current risk assessments should be updated to consider whether a transient substance lies upon the floor’s surface on a frequent and regular basis.  The threshold for what constitutes “frequent and regular” occurrence does not appear to be particularly high.  For example, in Ellis, there were only three falls in urine, involving employees within the three year period preceding the accident but such occurrence was found to be sufficiently frequent. 

This decision will have serious practical implications for the care professions where substances such as drink or food may be spilled on a “frequent and regular” basis.  If so, according to the decision in Ellis, the employer’s duty will be strict and the prospects of defending any such claims will be reduced.

Where possible, relying on evidence emanating from the above strategy, defendants should still seek to argue that the applicable duty falls within Regulation 12(3) which provides a less onerous duty to keep surfaces free from hazards “so far as reasonably practicable”.  Provided authorities operate a robust system of inspection / cleaning and have a good accident record, they may still be able to persuade a court that the occurrence of spillages is rare and that its duty falls under Regulation 12(3) rather than 12(1).

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SLIPS AND FALLS – SOME ARGUMENTS ABOUT MEASURING COEFFICIENTS OF FRICTION